Traffic accidents on a given section of roadway greatly increase while road work is performed in or near the roadway section. Lane restrictions, traffic speed fluctuations, bi-directional traffic flow, vehicles entering and exiting the roadway, and the general distracting surroundings of a work zone contribute to the propensity of accidents in and around roadway work zones. This propensity for accidents poses a very real risk to road construction crews, utility crews, maintenance workers, and other personnel in the vicinity of a work zone. It is not uncommon for accident rates to increase 50% or more during times of construction, and these accidents are increasingly causing injury and death to work zone personnel. Along with the human tragedy of the increased work zone related injuries and deaths, contractors suffer economically as well from worker's compensation rate increases, increased tort liability, and decreases in worker productivity and morale as work zone personnel pay greater attention to oncoming traffic and less attention to their work assignments.
Various devices and techniques are known which attempt to alert drivers to approaching roadway hazards. These devices were designed to make drivers more aware of their surroundings and/or to reduce the speed of vehicles approaching roadway hazards. These prior art techniques include: regulatory and advisory signage, dynamic speed limit signage, mock-up police cars, high visibility clothing, and traffic flow diversion devices, to name but a few. While these prior art devices and techniques undoubtedly deterred countless additional work zone related accidents, those devices are directed solely at alerting drivers of an approaching hazard. Those devices had no way to warn work zone personnel if or when a vehicle strayed from a designated traffic lane and breached the work zone perimeter.
A device is known which attempts to signal highway workers when an errant vehicle entered the work zone. However, the harsh environment of the roadway work zone proved too large an obstacle for this device to efficiently warn workers. The device comprises an infrared signal with a reflective cone, or an ultrasonic beam, to detect a vehicle passing thereby. The infrared signal or ultrasonic beam is positioned "upstream" from the work zone and is placed at 90.degree. to the oncoming traffic. This detector is in communication via a wireless data link to a 120 decibel siren positioned within the work zone. When a vehicle is detected upstream, a signal is transmitted to the siren and the siren sounds an audible warning. Another embodiment of this device uses a pneumatic tube laid across the roadway in place of the infrared or ultrasonic beam.
The problems with this warning device are numerous. First, most work zones are very noisy. In addition to the traffic noise and wind along any stretch of roadway, many work zones use heavy construction machinery, and jackhammers, shot blasters, and concrete cutters which create a tremendous amount of noise. Because Occupational Safety and Health Administration ("OSHA") standards required operators of this machinery to wear hearing protection, the operators were unable to hear the audible warning over the noise of the equipment they were operating and through their hearing protection. Further, even without hearing protection, personnel in the vicinity of this machinery and equipment often did not hear the audible warning.
Second, this warning device suffers several integrity problems. Because the device uses a single detector positioned "upstream" from the work zone and at 90.degree. to approaching traffic, it is possible for vehicles to enter the work zone without tripping the detector. Moreover, the heat and audible noise produced by work zone equipment and passing traffic would interfere with the prior art infrared and ultrasonic detectors causing false detections. Further, the distance between the detector and the siren necessitated a wireless data link therebetween. Modern work zones are flooded with electromagnetic noise within the popular communication frequencies. The frequent use of walkie-talkies by work zone personnel, portable and cellular telephones by work zone personnel and passing traffic, and CB and short wave radio by passing vehicular and air traffic would trigger the siren causing a significant problem with false alarms. Furthermore, this transmission required FCC compliance as well.
The present invention overcomes the foregoing problems by providing an intrusion alarm including a detector and a device for producing an optical warning signal to provide a visual warning when vehicles enter the work zone. The detector comprises a plurality of transmitter-sensor pairs connected in series along the work zone perimeter adjacent to active traffic. This serial connection detects vehicles breaching the work zone perimeter regardless which transmitter-sensor pair the vehicle passes between, thereby eliminating the risk of an errant vehicle from the active lane entering the work zone undetected.
The optical warning signal includes a primary strobe and a plurality of relay strobes arranged throughout the work zone. The primary strobe and relay strobes each include an illuminator capable of generating light flashes at a predetermined flash rate. The relay strobes also include a photoelectric sensor which detects light flashes at the predetermined flash rate. The primary strobe is electrically connected to the sensor of the transmitter-sensor pair farthest downstream. The primary strobe is activated upon a vehicle passing between any of the serially connected transmitter-sensor pairs. When activated, the primary strobe illuminator begins flashing at the predetermined flash rate. The photoelectric sensor of at least one relay strobe detects the predetermined flash frequency and activates its relay illuminator which flashes light at the predetermined flash rate thereby activating at least one other relay strobe. This cascading effect continues until the entire work zone is saturated with flashing light. The relay strobe can be portable so that work zone personnel positioned behind a barrier or operators required to look downward a high percentage of the time can place the strobe in their close proximity.
Generally, the method of this invention comprises serially connecting the plurality of transmitter-sensor pairs along a section of the work zone perimeter, energizing the primary strobe illuminator upon detection of a vehicle by the transmitter-sensor pair, and energizing each relay strobe when the relay strobe photo sensor detects light flashes at the predetermined flash rate. Again, the flashing light of each strobe (primary and relay) effectively warns work zone personnel within the vicinity of the strobe that a vehicle has breached the work zone perimeter, and triggers the upstream relay strobe creating a cascading effect.
The assembly and method of the present invention are significant improvements over the prior art in that the optical warning signal effectively alerts all work zone personnel of a vehicle breaching the work zone perimeter and is free from the interference caused by the excessive noise inherent with construction/maintenance machinery and equipment. Further, the portable nature of the strobe relay units allows them to be placed in close proximity to clusters of workers, workers behind obstructions, or workers required to focus their attention elsewhere. Moreover, because the strobe relays are activated by a predetermined optical repeating flash of light, it is unaffected by the electromagnetic noise inherent in and around work zones. This eliminates false alarms caused by other electromagnetic noise and eliminates a need for FCC compliance. Furthermore, because this intrusion alarm detects vehicles along the entire work zone perimeter adjacent to approaching traffic, the detection integrity of the work area is greatly enhanced over that of the prior art.
The present invention provides a highly reliable vehicle detection system which provides an immediate alarm capable of perception by all work zone personnel which is well suited for the harsh roadway work zone environment. Along with the reduction of work zone personnel injuries and deaths, the worker peace of mind translates into higher productivity.